This invention relates to a bendable tube for an endoscope, a catheter or the like, and a method for manufacturing the same.
In general, an endoscope includes a main body, an elongated insertion portion extending from the main body and a bendable tube disposed at a distal end of the insertion portion and remote controlled from the main body. The bendable tube includes a plurality of tubular joint pieces arranged in a row. Each joint piece is provided at one end portion thereof with one pair of first connecting portions and at the other end portion with one pair of second connecting portions. The first connecting portions are projected in a center axis direction of the joint piece and arranged 180 degrees away from each other in a peripheral direction and the second connecting portions are projected in the opposite direction to the first connecting portions and arranged 180 degrees away from each other in the peripheral direction. The first and second connecting portions of the adjacent joint pieces are overlapped with each other in a radical direction and rotatably connected together by a rivet (shaft member). Owing to this arrangement, the entire bendable tube can be bent.
In recent years, a thinner design of a bendable tube has been demanded. In line with this demand, the joint piece is also demanded to be miniaturized in diameter. For example, it is demanded that the joint piece is designed to have a diameter of about 1 to 2 mm or even smaller. However, in the above-mentioned general construction, the more the diameter of the joint piece is designed to be small, the more the connecting work using a rivet becomes difficult to perform. Thus, in a bendable tube disclosed in Japanese Patent Publication No. 2,619,949, a first connecting portion is formed with a through-hole and a second connecting portion is provided with a protruding element projecting in an axial direction of a joint piece. The protruding element is inserted into the through-hole and bent 180 degrees. By this, the adjacent joint pieces are connected together without a need of a rivet.
In the bendable tube disclosed in the above Publication, a thinner design is made possible because there is no need of a provision of a rivet, but there is involved such a problem that the bending operation is difficult to make because the frictional resistance is large between the protruding element and the through-hole.
It is an object of the present invention to provide a bendable tube in which adjacent joint pieces are connected without a need of a rivet thereby enabling to make a thinner design of the bendable tube and in which a smooth bending operation can be obtained.
It is another object of the present invention to provide a method for easily manufacturing a bendable tube having a thinner design in which a bending operation can be made smoothly without a need of a rivet.
A bendable tube according to the present invention includes, as a basic constitution, a plurality of tubular joint pieces arranged in a row. Each of the joint pieces is provided at one end portion thereof with a pair of first connecting portions and at the other end portion with a pair of second connecting portions. The first connecting portions are projected in a center axis direction of the joint piece and arranged 180 degrees away from each other in a peripheral direction and the second connecting portions are projected in the opposite direction to the first connecting portions and arranged 180 degrees away from each other in the peripheral direction. Moreover, in the bendable tube of the present invention, each of the first connecting portions is formed with a retaining portion having an inner periphery at least a part of which is arcuate and each of the second connecting portions is formed with a protrusion. The first and second connecting portions are connected together only by fitting engagement between the protrusion and the retaining portion. The first and second connecting portions are able to rotate relative to each other due to rubbing relation between an inner periphery of the retaining portion and an outer periphery of the protrusion. As a result, a rivet as a connecting means can be eliminated. Moreover, the friction between the first and second connecting portions can be made comparatively small and the bendable tube can easily be bent.
Preferably, the first connecting portion is arranged radially inside and the second connecting portion is arranged radially outside, the protrusion being projected radially inward from the second connecting portion so as to be fitted into the retaining portion of the first connecting portion. This constitution is suited to be employed when the protrusion is formed by pressing.
Preferably, at least a part of the outer periphery of the protrusion is arcuate. The rubbing relation between the outer periphery of the protrusion and the arcuate inner periphery of the retaining portion ensures a smooth relative rotation of the first ::and second connecting portions.
Preferably, the inner periphery of the retaining portion is a perfect circle. This feature ensures a more smooth relative rotation between the first and second connecting members.
The retaining portion may be composed of a circular through-hole. This through-hole allows the insertion of the protrusion. In the case where the protrusion includes a cylindrical peripheral wall, a smooth relative rotation between the first and second connecting portions is ensured. By providing an annular engagement portion engageable with a peripheral edge of the through-hole at a distal end of the peripheral wall of the protrusion, a reliable connection between the first and second connecting portions can be obtained.
The retaining portion and the protrusion may have a cylindrical peripheral wall and a bottom wall, which walls are rubbed with each other.
In a first embodiment of a method for manufacturing a bendable tube according to the present invention, a first connecting portion of a joint piece is preliminarily formed with a through-hole. In the joint pieces to be placed adjacent to each other, the second connecting portion of one of the adjacent joint pieces is radially externally overlapped with the first connecting portion of the other adjacent joint piece and the second connecting portion is pressed from outside, thereby forming a protrusion projecting inward in a radial direction and fitting into the through-hole. The joint pieces are rotatably connected together only by this fitting engagement between the protrusion and the through-hole. In this way, a very thin bendable tube can be manufactured easily, at a low cost and in a short time.
In a second embodiment of a method for manufacturing a bendable tube according to the present invention, in the joint pieces to be placed adjacent to each other, the second connecting portion of one of the adjacent joint pieces is radially externally overlapped with the first connecting portion of the other adjacent joint piece and such overlapped first and second connecting portions are pressed altogether from outside, thereby forming a circular recess in an outer peripheral surface of the first connecting portion and a circular protrusion on the second connecting portion simultaneously, the circular protrusion being projected inward in a radial direction and fitted into the retaining portion, the joint pieces being rotatably connected together only by this fitting engagement between the protrusion and the recess. In this way, a very thin bendable tube can be manufactured easily, at a low cost and in a short time.